Medical Issues

Chytridiomycosis In Amphibians

Chytridiomycosis In Amphibians

Chytridiomycosis, an infection of amphibians caused primarily by the fungus Batrachochytrium Dendrobatidis Bd. This is a new disease that has a significant impact on amphibian populations around the world. 
Over 200 amphibian and frog species have been decimated or wiped out by the disease.The chytrid fungal Batrachochytrium Dendrobatidis is responsible for this potentially fatal skin disease. It has been found on amphibians from over 35 countries. The chytrid is a fungus that can cause sporadic death in some amphibian species and 100% mortality in others. It is thought that this disease has caused amphibian populations to decline in Australia, South America and North America.

Chytrids & Chytridiomycosis In Amphibians

Chytrids are usually found in soil or water, but some live as parasites on insects and plants. The fungus reproduces in an asexual way and its spores move through water. Vertebrates are only infected by the amphibian-chytrid fungus. It is believed that frogs contract the disease by coming into contact with water containing spores of infected animals. The disease’s host is not known to cause death, nor is the way the fungus survives without amphibian populations.
It is not clear how this disease interacts other stressors, i.e. It is unclear how pollution, invasive species and climate change can exacerbate population declines. Pesticides, pollution and other pollutants can also reduce amphibian immunity response making them more vulnerable to infectious diseases. Climate change can alter parasite community dynamics by making conditions more conducive to pathogen growth. It may also reduce the immune defences of amphibians who are stressed and not coping well with suboptimal climate conditions.
Chytrid is a disease that affects over 350 amphibians. However, it seems to have the most severe impact onCHYTRIDIOMYCOSIS IN AMPHIBIANS frog species. The disease is not present in all frogs.Bd multiplies in the keratin of the skin by producing zoospores that are released into the environment. The can survive in water for up to a week depending on temperature.

The clinical signs of each species are different. Anorexia and Lethargy are the first signs of chytrid. The skin of most frogs is a gray-white, tan or opaque color.

Other signs of a disorder include convulsions (a reflex which corrects the body’s orientation after it is moved from its normal upright position), red skin, abnormal feeding behaviors, and discoloration around the mouth.

Bd is an airborne fungus which disperses in the environment to find a new host. The fungus enters the body through the skin after traveling through water sources.

Histopathologic examinations of dead animal tissues are required to diagnose true chytridiomycosis in amphibians.

The zoospores are widespread and it is not practical to treat amphibians outside. No vaccine exists.

Chytridiomycosis in amphibians can be spread easily by humans. Cleaning boots, clothing, and equipment is important. Wild amphibians shouldn’t be moved from habitat to habitat.

Diagnosis of Chytridiomycosis In Amphibians

Methods used to diagnose and treat Bd infection will depend on factors like the species involved, the number and type of animals, and the availability of resources. Wet mount and cytologic examinations can provide a rapid diagnosis of clinically important infections in a matter of minutes, while subclinical infection can only be diagnosed reliably by molecular techniques such as PCR. Although the PCR test is highly sensitive, subclinical low-level infections may require multiple tests to detect. Recent attention has been paid to the treatment of infected animals, including controlled experiments that tested safety and efficacy. The outcome of treatment is variable, depending on the animal, the life stage (e.g. tadpole, metamorph, adult) and the lab or institution that administers the treatment. Itraconazole and temperature elevation are the most commonly used treatment methods. Itraconazole baths have been used successfully, but require more experience with a larger range of species. 9 Good husbandry and good hygiene are essential for successful treatment. The use of chloramphenicol baths has been successful but requires more experience in a wider range of species.

Treatment Of Chytridiomycosis In Amphibians

Background information and DefinitionsPoisonous blue frog

The treatment of chytridiomycosis will ensure that amphibian breeding programmes are successful. To reduce the risk that the disease will spread when animals are transferred between wild and captive populations.

The Batrachochytrium Dendrobatidis chytrid fungus is sensitive to temperatures higher than 32degC. The fungus dies at 37degC in four hours, and at 47degC it takes only 30 minutes to kill (Young 2007). In a study, Rowley & Aford (2013) found that the risk of infection with chytrid by three species of frogs in the wild was significantly reduced with increased time spent at body temperatures over 25degC. In captivity, a study found that the risk of chytrid infection and death was lower for frogs housed at 27degC than those kept at 17degC or even 23degC. (50 vs. 100% mortality; Berger et. al. 2004, The treatment of chytridiomycosis may be achieved by increasing the temperature in amphibian housing.

Four-wheel Drive VehiclesFive studies in Australia, Switzerland, and the USA (including four replicated and controlled studies) found that raising water or enclosure temperature to 30degC over a period of 16 hours could cure frogs and tadpoles from chytridiomycosis. One can be a part of the other.Heat treatment of 30-35degC over 36 hours failed to cure the northern leopard frogs.

Itraconazole and miconazole baths (0.01 percent imidazole dissolved in 0.6% saline, 5 minutes per day for 11 days 80) seem to be effective treatments. The fungus persists in wild habitats, and it may be the cause of some amphibian population declines.

History Of Chytridiomycosis In AmphibiansDainty tree frogs sometimes sleep in waterlily flowers

The chytrid fungus Batrachochytrium Dendrobatidis, which is responsible for the disease, was first discovered in Queensland, Australia, in 1993. Since then, research has revealed that the fungus has spread across Australia. It has also been in the country since 1970. It is also present in Africa, Americas, Europe and New Zealand. Chytridiomycosis is found in Australia’s states, the Australian Capital Territory and the Northern Territory. It appears to be restricted to relatively cool, wet regions of Australia. These include the Great Dividing Range, adjacent coastal areas, eastern and central Tasmania and southern South Australia. There are only a few places in Australia that have a suitable host environment. These include the World Heritage Area of south-west Tasmania, and the Iron Range at Cape York. Due to the isolation of amphibian populations, there are pockets of disease-free zones within infected areas. Chytridiomycosis/B. Dendrobatidis has been listed in Australia’s National List of Reportable Diseases of Aquatic Animals, and in the Aquatic Animal Health Code of the World Organisation for Animal Health.

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